1. Field
The disclosed concept pertains generally to electrical switching apparatus and, more particularly, to electrical switching apparatus for controlling a load. The disclosed concept also pertains to protection relays, such as motor protection relays, and to systems including controllers for controlling loads.
2. Background Information
Contactors are employed, for example and without limitation, in starter applications to switch on/off a load as well as to protect a load, such as a motor or other electrical device, from current overloads. Contactors are used as electrical switching apparatus and incorporate fixed and movable contacts that when closed, conduct electric power.
A starter is a device used to provide protection and control for a load, such as a single-phase or three-phase motor and the like, typically used in, for example, various industrial settings to operate machinery. A common type of starter includes an electromagnetic contactor and a motor protection relay. The contactor includes separable contacts that are connected to each phase of the motor, such that, when closed, the separable contacts connect the motor to an electrical source, such as a three-phase electrical source. The motor protection relay monitors the load current and, in some cases, voltage, and trips the contactor open if a problem condition, such as persistent over current, arises. Typically, the motor protection relay tracks an I2t characteristic of the load current, which is a measure of heating. Motor protection relays typically include a microprocessor, which digitally generates the I2t value. When the calculated I2t value reaches a designated trip level, the contactor is tripped open to interrupt the flow of current to the motor.
For flash protection, NFPA 70 110.16 and NFPA 70E 400.11 require that switchboards, panelboards, industrial control panels, meter socket enclosures, and motor control centers that are in other than dwelling occupancies and are likely to require examination, adjustment, servicing, or maintenance while energized be field marked to warn qualified persons of potential electric arc flash hazards. The marking shall be located so as to be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment.
A known process of displaying an available fault current, an incident energy and a personnel protective equipment (PPE) level (e.g., without limitation, gloves; flame retardant garments) for a particular power system is for an engineer to perform theoretical calculations using power system parameters. Then, based on those theoretical calculations, a printed label is affixed to the power system equipment stating the manually calculated available fault current, the manually calculated incident energy and the manually calculated PPE level. There is, however, no known way to verify the correctness of this information. There is further the risk that if the power system is modified, the manually calculated available fault current, the manually calculated incident energy and the manually calculated PPE level will change, but the printed label will not be timely changed, if at all.
There is room for improvement in electrical switching apparatus.
There is also room for improvement in protection relays, such as motor protection relays.
There is further room for improvement in systems including controllers for controlling loads.